This invention relates to the display of still images that appear animated to a viewer in motion relative to the still images. More particularly, this invention relates to the display of such still images in spatially-constrained environments.
Display devices that display still images appearing to be animated to a viewer in motion are known. These devices include a series of graduated images (i.e., adjacent images that differ slightly and progressively from one to the next). The images are arranged in the direction of motion of a viewer (e.g., along a railroad) such that the images are viewed consecutively. As a viewer moves past these images, they appear animated. The effect is similar to that of a flip-book. A flip-book has an image on each page that differs slightly from the one before it and the one after it such that when the pages are flipped, a viewer perceives animation.
A longstanding trend in mass transportation systems has been the development of installations to provide the passengers in subway systems with animated motion pictures. The animation of these motion pictures is effected by the motion of the viewer relative to the installation, which is fixed to the tunnel walls of the subway system. Such installations have obvious value: the moving picture is viewable through the train windows, through which only darkness would otherwise be visible. Possible useful moving picture subjects could be selections of artistic value, or informative messages from the transportation system or from an advertiser.
Each of the known arrangements provides for the presentation of a series of graduated images, or xe2x80x9cframes,xe2x80x9d to the viewer/rider so that consecutive frames are viewed one after the other. As is well known, the simple presentation of a series of still images to a moving viewer is perceived as nothing more than a blur if displayed too close to the viewer at a fast rate. Alternatively, at a large distance or low speeds, the viewer sees a series of individual images with no animation. In order to achieve a motion picture effect, known arrangements have introduced methods of displaying each image for extremely short periods of time. With display times of sufficiently short duration, the relative motion between viewer and image is effectively arrested, and blurring is negligible. Methods for arresting the motion have been based on stroboscopic illumination of the images. These methods require precise synchronization between the viewer and the installation in order that each image is illuminated at the same position relative to the viewer, even as the viewer moves at high speed.
The requirements of a stroboscopic device are numerous: the flash must be extremely brief for a fast moving viewer, and therefore correspondingly bright in order that enough light reach the viewer. This requirement, in turn, requires extremely precisely timed flashes. This precision requires extremely consistent motion on the part of the viewer, with little or no change in speed. All of the aforementioned requirements result in a high level of mechanical or electrical complexity and cost, or greater consistency in train motion than exists. Other known arrangements have overcome the need for high temporal precision by providing a transponder of some sort on the viewer""s vehicle and a receiver on the installation to determine the viewer""s position. These arrangements involve considerable mechanical and electrical complexity and cost.
The aforementioned known arrangements generally require the viewer to be in a vehicle. This requirement may be imposed because the vehicle carries equipment for timing, lighting, or signalling; or because of the need to maintain high consistency in speed; or to increase the viewer""s speed, for example. The use of a vehicle requires a high level of complexity of the design because of the number of mechanical elements and because one frequently is dealing with existing systems, requiring modification of existing equipment. The harsh environment of being mounted on a moving subway car may limit the mechanical or electrical precision attainable in any unit that requires it, or it may require frequent maintenance for a part where high precision has been attained.
The use of a vehicle also imposes constraints. At the most basic level, it limits the range of possible applications to those where viewers are on vehicles. More specifically, considerations of the vehicle""s physical dimensions constrain a stroboscopic device""s applicability. The design must take into account such information as the vehicle""s eight and width, its window size and spacing, and the positions of viewers within the vehicle. For example, close spacing of windows on a high speed train requires that stroboscopic discharges preferably be of high frequency and number in order that the display be visible to all occupants of a train. The dimensions of the environment, such as the physical space available for hardware installation in the subway tunnel and the distances available over which to project images, impose further constraints on the size of elements of any device as well as on the quality and durability of its various parts.
Though in principle a stroboscopic device can work for slowly moving viewers, simply by spacing the projectors more closely, in practice it is difficult. First, closer spacing increases cost and complexity. Also, once the device is installed with a fixed projector-to-projector distance, a minimum speed is imposed on the viewer.
An existing method for the display of animated images involving relative motion between the viewer and the device is the zootrope. The zootrope is a simple hollow cylindrical device that produces animation by way of the geometrical arrangement of slits cut in the cylinder walls and a series of graduated images placed on the inside of the cylinder, one per slit. When the cylinder is spun on its axis, the animation is visible through the (now quickly moving) slits.
The zootrope is, however, fixed in nearly all its proportions because its cross section must be circular. Since the animation requires a minimum frame rate, and the frame rate depends on the rotational speed, only a very short animation can be viewed using a zootrope. Although there is relative motion between the viewer and the apparatus, in practice the viewer cannot comfortably move in a circle around the zootrope. Therefore only one configuration is practicable with a zootrope: that in which a stationary viewer observes a short animation through a rotating cylinder.
For the reasons of its incapacity to be altered in shape, the short duration of its animation, and the fact that it must be spun, the zootrope has remained a toy or curiosity without practical application. However, at least one known system displays images along an outdoor railroad track in an arrangement that might be referred to as a xe2x80x9clinear zootropexe2x80x9d in which the images are mounted behind a wall in which slits are provided. That outdoor environment is essentially unconstrained.
In view of the foregoing, it would be desirable to be able to provide apparatus for use in a spatially-constrained environment that displays still images that appear animated to a viewer in motion.
It would also be desirable to be able to provide such apparatus for use in a spatially-constrained environment having low ambient lighting levels.
It is an object of this invention to attempt to provide apparatus for use in a spatially-constrained environment that displays still images that appear animated to a viewer in motion.
It is also an object of this invention to attempt to provide such apparatus for use in a spatially-constrained environment having low ambient lighting levels.
In accordance with this invention, there is provided apparatus for displaying a plurality of still images, forming an animated display, to a viewer moving substantially at a known velocity relative to said still images substantially along a known trajectory substantially parallel to said still images. The apparatus includes a backboard having a backboard length along the trajectory. The still images are mounted on a surface of the backboard, with each of said still images having an actual image width and having an image center. Image centers of adjacent images are separated by a frame-to-frame distance. A slitboard is positioned substantially parallel to the backboard, facing said surface thereof and separated therefrom by a board-to-board distance. The slitboard is mounted at a viewing distance from the trajectory. The board-to-board distance and the viewing distance total a backboard distance. The slitboard has a slitboard length along the trajectory, and has a plurality of slits substantially perpendicular to the slitboard length. Each slit corresponds to one of the images and has a slit width measured along the slitboard length and a slit center, respective slit centers of adjacent ones of the slits being separated by the frame-to-frame distance. In order to display each image with an apparent image width, the board-to-board distance, the viewing distance and the actual image width are selected so that the product of (a) the actual image width and (b) the quotient of (i) the viewing distance and (ii) the board-to-board distance substantially equals the apparent image width. In order to project each image substantially without blurring, the slit width is selected to be at most about one-tenth of the actual image width.